#include<stdio.h>
#include<iostream>
#include<string.h>
#include<math.h>
#include<algorithm>
using namespace std;
int main()
{
	double x1, x2, x3, y1, y2, y3;
	while (cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3)
	{
		printf("%.1lf\n", 0.5 * fabs((x2 - x1)*(y3 - y2) - (x3 - x2)*(y2 - y1)));
	}
	return 0;
}